Cytochalasin B-binding and transport properties of the Glut1 human red cell glucose transporter

• The mechanism by which the D-glucose transporter Glut1 facilitates transport of monosaccharides, dehydroascorbic acid and possibly nicotinamide across membranes toward lower chemical activity is thought to involve binding of the substrate at the internal or external face of the protein followed by a thermally triggered conformational change that allows release of the substrate from a binding site exposed at the opposite side of the protein. In the presumably tetrameric transporter in the cell membrane, pairs of identical subunits may work in concert. In each dimer, one of the subunits may expose an external substrate-binding site and the other an internal site at a given moment (State 1). Only the internal site binds the inhibitor cytochalasin B. Cytochalasin B-binding analyses and transport data support this mechanism [Hamill, S., Cloherty, E.K., and Carruthers, A. 1999, Biochemistry, 38, 16974]. Both alkaline disulfide reduction of Glut1 in the cell membrane and polylysine-coating of red cells convert Glut1 to a functionally monomeric state that offers a cytochalasin B-site on every subunit (State 2). Cysteine-scanning mutagenesis experiments with transport and inhibition analyses indicate that the proposed transmembrane segments 5 and 7 are amphipathic α-helices that probably line the glucose permeation pathway. The future determination of the 3D structures of sugar transporters may elucidate the transport mechanism and subunit interactions.

Publikations- och innehållstyp

ref (ämneskategori)

kap (ämneskategori)